The present invention relates generally to a retaining formation for the connection of components in a brake. Specifically, the present invention relates to a retaining clip for the connection of a push rod in an actuator to a lever of an air disc brake.
It is known in brake applications to operate levers such as op-shafts and adaptors with push rods. The push rods act in compression when an actuating force is applied (e.g., by the activation of the brake) and transmit compressive forces in an actuation stroke, for example, between: an actuator and an op-shaft for actuation of a brake, an actuator and an adaptor lever for rotation of the adaptor lever, and an adaptor lever and an op-shaft for actuation of a brake.
The push rod then returns via a return stroke as air pressure is released and a return spring takes over. In brake applications, the return stroke occurs as a result of the actuating force being removed (e.g., by release of the brake by a driver) and additionally the lever providing a return force on the push rod (as most brakes provide a return mechanism to prevent the brake from remaining engaged).
Levers such as op-shafts and adaptor levers rotate in use. The end of the lever on which the push rod acts is positioned away from a pivot axis of the lever, and the contact point at which the push rod contacts the lever will tend to have a component of motion in a plane perpendicular to a main axis of the push rod.
If the push rod is to be attached to the lever, the end of the push rod that contacts the lever needs to be able to articulate in the plane perpendicular to the main axis of the push rod at the same time as the lever. This may be achieved by rotatably mounting the push rod about both ends, i.e., both at the contact point and at and end distant from the contact point. In the instance of an actuator push rod, the actuator lever itself may be rotatably mounted to achieve this.
The push rod may be rotatably mounted to the lever at the contact point by simply providing a socket on the lever and a ball on the end of the push rod. The push rod is constrained from movement away from the contact point on the lever (by the walls of the cup), but is able to slide rotationally providing the desired motion in use.
This solution is problematic, as in certain situations, the push rod can return before the lever. This may occur if, for example, the brake is operating in cold weather conditions. If the brake actuator is released, the brake push rod returns. However, the brake mechanism may be slow to respond due to the low temperature causing increased viscosity in the lubricant. The push rod and the lever can become disengaged and misaligned such that on a subsequent actuation stroke, the push rod either contacts the lever at the incorrect position, or does not contact it at all.
Alternatively, a pinned joint is known. A pin is then inserted through a corresponding series of bores in the lever and push rod to pin the push rod to the lever, allowing relative rotation about an axis parallel to a lever rotation axis. However, this arrangement requires modifications to the manufacture of both the lever and the push rod (i.e., the formation of the bores) and increases part count (in the need for a pin). The complexity and cost of assembly and servicing the brake is also increased due to the need to fit and remove the pin in a confined space.
Additionally, one of the corresponding bores is often of relatively large diameter compared to the pin to allow free movement of the push rod relative to the lever at the extreme ends of the range of motion of the lever. This may result in misalignment of the push rod and lever and jamming of the brake.
It is an aim of the present invention to overcome or at least mitigate one or more of these problems.